Optical element light emitting device and method of manufacturing optical element

ABSTRACT

The present invention relates to an optical element for converting light of prescribed wavelength emitted from a light source into light of wavelength different from the prescribed wavelength for outputting. A first crystal part ( 20 ) and a second crystal part ( 21 ) having respective surfaces opposed to each other whose coefficients of linear expansion are different by 5 ppm or more are optically polished so that the surfaces opposed to each other include crystallographic axes. An acrylic adhesive whose glass transition point is 75° C. or lower is applied to the adhesive surface of the first crystal part ( 20 ) or the second crystal part ( 21 ) to stick the first crystal part ( 20 ) and the second crystal part ( 21 ) to each other. The adhesive is irradiated with light to cure the adhesive and form an adhesive layer ( 22 ) having a refractive index of 1.52 or lower. Then, the first crystal part and the second crystal part stuck to each other are cut into a desired size to form the optical element. In the optical element, the separation of the adhesive layer ( 22 ) for connecting the first crystal element to the second crystal element and the damage of the crystal parts are suppressed.

TECHNICAL FIELD

[0001] The present invention relates to an optical element forperforming a wavelength conversion of light by using a non-linearoptical phenomenon, a light emitting device for emitting light whosewavelength is converted by using the optical element and a method forproducing the optical element.

[0002] This application claims a priority based on Japanese PatentApplication No. 2002-186697 filed one Jun. 26, 2002 in Japan. Theearlier application is applied to this application by referring to it.

BACKGROUND ART

[0003] As a compact short wavelength laser or a wavelength conversionlaser, there is an OPO (Optical Parametric Oscillator) laserrepresentative of an SHG (Second Harmonic Generation) laser using anon-linear optical crystal. This laser has a laser beam of a prescribedwavelength as a basic beam, converts the basic beam into a laser beamhaving a wavelength different from the wavelength of the basic beam andoutputs the converted beam. The laser that performs the above-describedwavelength conversion is used as various kinds of light sources of anoptical disc device or an optical communication module or the like.

[0004] Such a laser employs a method that a solid-state laser crystal isprovided in an internal cavity type OPO laser in which a non-linearoptical crystal is disposed in a cavity and a laser beam outgoing from asemiconductor laser is allowed to be incident on the end face of thesolid-state laser crystal side to pump the solid-state laser crystal andgenerate the basic light.

[0005] In this case, the above-described laser comes into contact withor sticks to all optical elements disposed in the cavity to form thecavity by the end face of the input side of the laser beam and the endface of the output side of the laser beam. Thus, a device can be madecompact. Further, the optical elements may not need to be adjusted, thedevice can be applied to various kinds of uses. Further, not only theabove-described laser can be made compact, but also conversionefficiency can be improved by repeatedly reflecting the basic beam inthe cavity.

[0006] In a method for producing an optical element used in such alaser, relatively large wafer type two crystal parts are stuck to eachother by an adhesive, and then, an optical film or the like is formedand the obtained product is cut into chips.

[0007] In this method, since the wafers can be stuck to each other undera state that the warp of the wafers due to the stress of the opticalfilm is not produced, an adhesive layer having a uniform thickness canbe obtained. Accordingly, not only various types of characteristics ofoptical parts can be improved, but also unevenness in characteristics ofthe cut chips can be suppressed.

[0008] In the above-described method for producing the optical element,the adhesive layer is exposed to high temperature upon formation of theoptical film. Thus, the adhesive layer may be possibly peeled off or thedamage of the crystal parts may be caused due to the difference incoefficient of linear expansion between the two crystal parts.

[0009] In the laser for generating the basic beam under the pumping bythe laser beam from the semiconductor laser, the laser beam heats theoptical elements. Accordingly, when the output of the laser beam israised, the adhesive layer is peeled off or the two crystal parts arebroken owing to the difference in coefficient of linear expansionbetween the two crystal parts.

[0010] Especially, when the two crystal parts greatly different incoefficient of linear expansion are stuck to each other, the peel-off ofthe adhesive layer or the damage of the crystal parts is outstandinglygenerated.

[0011] As a cause that the above-described adhesive layer is peeled offor the crystal parts are broken, a below-described phenomenon isconsidered. When the two crystal parts greatly different in coefficientof linear expansion are stuck to each other and exposed to hightemperature under a condition that the two crystal parts are stuck toeach other, a stress is generated in the adhesive layer due to thedifference in coefficient of linear expansion. When the adhesive layermitigates this stress, the adhesive layer will not be peeled off, nor abase will be broken. When the adhesive layer cannot mitigate the stress,the peel-off or the damage will be firstly generated from parts whosestrength is lowest. Whether or not the adhesive layer is separated fromthe crystal parts or whether or not the crystal parts are broken isdetermined depending on the relation between the adhesive strength ofthe adhesive layer and the brittleness of the crystal parts. Here,whether or not the adhesive layer can mitigate the stress is determineddepending on the mechanical materiality of the adhesive layer in whichthe adhesive is cured and a geometric factor including the thickness ofthe adhesive layer and an adhesive area.

DISCLOSURE OF THE INVENTION

[0012] It is an object of the present invention to provide a new opticalelement capable of solving the problems of the above-described opticalelement, a light emitting element using this optical element and amethod for producing an optical element.

[0013] It is another object of the present invention to provide anoptical element in which an adhesive layer is not peeled off or crystalparts are broken due to the difference in coefficient of linearexpansion and a light emitting device having this optical element.

[0014] It is a still another object of the present invention to providea method for producing an optical element in which the peel-off of anadhesive layer or the damage of crystal parts due to the difference incoefficient of linear expansion is not generated.

[0015] In order to achieve the above-described objects, an opticalelement according to the present invention serves to convert lighthaving a prescribed wavelength emitted from a light source into light ofwavelength different from the prescribed wavelength and output the lightwith the converted wavelength. The optical element comprises a firstcrystal part including KTiOPO₄ or quartz; a second crystal partincluding YVO₄ doping Nd, and an adhesive layer by which the firstcrystal part is stuck to the second crystal part. Surfaces of the firstcrystal part and the second crystal part opposed to each other throughthe adhesive layer have coefficients of linear expansion which aredifferent by 5 ppm or more and the surfaces opposed to each otherthrough the adhesive layer are disposed so as to includecrystallographic axes. The adhesive layer is formed by curing an acrylicadhesive whose glass transition point is 75° C. or lower by applyinglight to the adhesive, wherein the refractive index of the adhesivelayer after cure is 1.52 or lower.

[0016] In the optical element according to the present invention, thefirst crystal part and the second crystal part having respectivesurfaces opposed to each other whose coefficients of linear expansionare different by 5 ppm or more are disposed so that the surfaces opposedto each other include crystallographic axes. An acrylic adhesive whoseglass transition point is 75° C. or lower is applied to the surface ofthe first crystal part or the second crystal part to allow the firstcrystal part to abut on the second crystal part. The adhesive isirradiated with light to cure the adhesive. Thus, the separation of anadhesive layer or the damage of the first crystal part and/or the secondcrystal part due to the difference in coefficient of linear expansionbetween the mutually opposed surfaces of the first crystal part and thesecond crystal part can be suppressed.

[0017] A light emitting device according to the present inventioncomprises: a light source for emitting light of prescribed wavelength;and an optical element including a first crystal part including KTiOPO₄or quartz; a second crystal part including YVO₄ doping Nd; and anadhesive layer by which the first crystal part is stuck to the secondcrystal part; and converting light of wavelength emitted from a lightsource into light of wavelength different from the prescribed wavelengthfor outputting. Surfaces of the first crystal part and the secondcrystal part opposed to each other through the adhesive layer havecoefficients of linear expansion which are different by 5 ppm or more.The surfaces opposed to each other through the adhesive layer aredisposed so as to include crystallographic axes. The adhesive layer isformed by curing an acrylic adhesive whose glass transition point is 75°C. or lower by applying light to the adhesive, wherein the refractiveindex of the adhesive layer after cure is 1.52 or lower.

[0018] In the light emitting device according to the present invention,the first crystal part and the second crystal part having respectivesurfaces opposed to each other whose coefficients of linear expansionare different by 5 ppm or more are disposed so that the surfaces opposedto each other include crystallographic axes. An acrylic adhesive whoseglass transition point is 75° C. or lower is applied to the surface ofthe first crystal part or the second crystal part to allow the firstcrystal part to abut on the second crystal part. The adhesive isirradiated with light to cure the adhesive. Thus, the separation of anadhesive layer or the damage of the first crystal part and/or the secondcrystal part due to the difference in coefficient of linear expansionbetween the mutually opposed surfaces of the first crystal part and thesecond crystal part can be suppressed.

[0019] In a method for producing an optical element according to thepresent invention, the method for producing the optical element forconverting light of prescribed wavelength emitted from a light sourceinto light of wavelength different from the prescribed wavelength foroutputting comprises: a polishing step of optically polishing a firstcrystal part including KTiOPO₄ or quartz and a second crystal partincluding YVO₄ doping Nd so that surfaces opposed to each other havecoefficients of linear expansion different by 5 ppm or more and thesurfaces opposed to each other include crystallographic axes; anapplying step of applying an acrylic adhesive whose glass transitionpoint is 75° C. or lower to the surface of the first crystal part or thesecond crystal part; a sticking step of allowing the first crystal partto abut on the second crystal part through the adhesive applied in theapplying step and irradiating the adhesive with light to cure theadhesive and form an adhesive layer having a refractive index of 1.52 orlower; and a cutting step of cutting the first crystal part and thesecond crystal part stuck to each other through the adhesive layer to adesired size.

[0020] In the method for producing an optical element according to thepresent invention, the first crystal part and the second crystal parthaving respective surfaces opposed to each other whose coefficients oflinear expansion are different by 5 ppm or more are disposed so that thesurfaces opposed to each other include crystallographic axes. An acrylicadhesive whose glass transition point is 75° C. or lower is applied tothe surface of the first crystal part or the second crystal part toallow the first crystal part to abut on the second crystal part. Theadhesive is irradiated with light to cure the adhesive and stick thefirst crystal part to the second crystal part. The first crystal partand the second crystal part stuck to each other is cut to an opticalelement of a desired size. In the optical element produced in such amanner, the separation of an adhesive layer or the damage of the firstcrystal part and/or the second crystal part due to the difference incoefficient of linear expansion between the first crystal part and thesecond crystal part can be suppressed.

[0021] Still other objects of the present invention and specificadvantages obtained by the present invention will be more apparent fromthe explanation of embodiments described below by referring to thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022]FIG. 1 is a side view showing the structure of a laser pointer towhich the present invention is applied.

[0023]FIG. 2 is a diagram showing the decided results of samples ofadhesives respectively forming adhesive layers of wavelength convertingelements.

[0024]FIG. 3 is a diagram showing the decided results in which acrylicsamples of the samples of the adhesives forming the adhesive layers ofthe wavelength converting elements are arranged in order of glasstransition points Tg.

[0025]FIG. 4 is a diagram showing the acrylic samples of the samples ofthe adhesives forming the adhesive layers of the wavelength convertingelements and the samples whose glass transition points are 75° C. orlower are arranged in order of refractive indexes nD after the adhesivesare cured.

BEST MODE FOR CARRYING OUT THE INVENTION

[0026] Now, an embodiment of the present invention applied to a laserpointer will be described below.

[0027] The laser pointer to which the present invention is applied canconvert the wavelength of a laser beam emitted from a semiconductorlaser and output a laser beam having shorter wavelength. A user canindicate a desired position by the laser beam.

[0028] Here, an ordinary laser pointer serves to apply the laser beam ofa red wavelength band having about 600 nm or longer. The laser pointerto which the present invention is applied emits the laser beam of agreen wavelength band of about 500 nm having a higher visibility thanthat of the red wavelength band.

[0029] The laser pointer 1 to which the present invention is appliedcomprises, as shown in FIG. 1, a semiconductor laser 10 for emitting alaser beam, a wavelength converting element 11 for converting the laserbeam emitted from the semiconductor laser 10 and outputting theconverted laser beam, an emitting lens 12 for shaping the form of thebeam of the laser beam converted by the wavelength converting element11, and a battery 13 for supplying electric power to drive thesemiconductor laser 10.

[0030] The semiconductor laser 10 is a semiconductor laser for emittinga laser beam having, for instance, the wavelength of about 808 nm.

[0031] The wavelength converting element 11 is an element for convertingthe wavelength of a laser beam emitted from the semiconductor laser 10to output the laser beam of about 532 nm (refer it to as a convertedbeam, hereinafter.).

[0032] The emitting lens 12 is a lens element provided so as to shapethe form of the beam of the converted beam. In the emitting lens 12, forinstance, a position in the direction of an optic axis can be adjustedso as to adjust a beam radius.

[0033] The battery 13 is the battery for supplying electric power fordriving the semiconductor laser 10. In order to make the structure ofthe laser pointer 1 compact, a compact battery is employed. When thecasing of the laser pointer 1 described below is formed in asubstantially cylindrical shape, the battery 13 is preferably configuredin a cylindrical shape so that the battery is accommodated in thecasing.

[0034] In the laser pointer 1 constructed as described above, thesemiconductor laser 10, the wavelength converting element 11, theemitting lens 12 and the battery 13 are fixed in the casing not shown inthe drawing. The laser pointer 1 is formed, for instance, in asubstantially cylindrical shape, what is called, a pen type shape.

[0035] The wavelength converting element 11 includes a first crystalpart 20, a second crystal part 21, an adhesive layer 22 formed by curingan adhesive between the first crystal part 20 and the second crystalpart 21, and a first selective transmitting film 23 and a secondselective transmitting film 24 as a pair of optical films between whichthe first crystal part 20 and the second crystal part 21 to form acavity.

[0036] The first crystal part 20 is made of, for instance, YVO₄ (YttriumVanadate) doped with neodymium. The laser beam that passes through thefirst selective transmitting film 23 is allowed to be incident on thefirst crystal part 20 to output the laser beam having the wavelength ofabout 1064 nm (refer it to as a basic beam) pumped by the laser beam.

[0037] The second crystal part 21 is made of, for instance, KTiOPO₄(refer it to as KTP, hereinafter.), converts the basic beam outputtedfrom the first crystal part 20 to the laser beam having the wavelength ½as long as the above-described wavelength, that is, the converted beamby the SHG and outputs the converted beam of about 532 nm to the secondselective transmitting film 24.

[0038] The first crystal part 20 and the second crystal part 21 havesurfaces opposed to each other whose coefficients of linear expansionare different by 5 ppm or more. The first and second crystal parts 20and 21 are disposed so that the surfaces including their c-axes areopposed to each other to obtain optimum conditions for performing aphase matching by the SHG.

[0039] Here, in the case of the wavelength converting element 11 usedfor the SHG laser, YVO₄ is stuck to KTP. As for the relation of theircrystallographic axes, since the c-axis of the KTP and the a/c combinedaxis of the YVO₄ are stuck to each other, the difference in coefficientof linear expansion between them becomes large like −0.65 (KTP)−7.9(YVO₄)=8.55 ppm.

[0040] The adhesive layer 22 is formed by irradiating an acrylicadhesive having light transmitting characteristics and a glasstransition point Tg of about 75° C. or lower with ultraviolet rays orvisible rays and by curing the adhesive, and has its refractive index ofapproximately 1.52 or lower. Especially, the adhesive layer 22 has ahigh transmittance relative to at least the wavelengths of theabove-described laser beam and the basic beam.

[0041] The first selective transmitting film 23 is an optical filmprovided so as to transmit the laser beam and reflect the basic beam,and designed to have different transmittances and reflectances inaccordance with the wavelengths of the laser beam and the basic beam.That is, the first selective transmitting film 23 allows the laser beamhaving the wavelength of about 808 nm to be transmitted and the laserbeam having the wavelength of about 1064 nm to be reflected inaccordance with the relation between the semiconductor laser 10, thefirst crystal part 20 and the second crystal part 21.

[0042] The second selective transmitting film 24 is an optical filmprovided so as to pass the basic beam and reflect the converted beam,and designed to have different transmittances and reflectances inaccordance with the wavelengths of the basic beam and the convertedbeam. That is, the second selective transmitting film 24 allows thelaser beam having the wavelength of about 1064 nm to be transmitted andthe laser beam having the wavelength of about 532 nm to be reflected inaccordance with the relation between the semiconductor laser 10, thefirst crystal part 20 and the second crystal part 21.

[0043] Now, an optical path in which the laser beam emitted from thesemiconductor laser 10 is emitted as the converted beam in the laserpointer 1 having the wavelength converting element 11 constructed asdescribed above will be described below.

[0044] The laser beam having the wavelength of about 808 nm emitted fromthe semiconductor laser 10 is made incident on the wavelength convertingelement 11 from the first selective transmitting film 23, passes throughthe first selective transmitting film 23 to be incident on the firstcrystal part 20 and pumps the first crystal part 20 to generate thebasic beam having the wavelength of about 1064 nm.

[0045] Then, the basic beam having the wavelength of substantially 1064nm outputted from the first crystal part 20 is incident on the adhesivelayer 22 to pass through the adhesive layer 22. Then, the basic beam isincident on the second crystal part 21 to convert the wavelength in aprescribed conversion efficiency by the second crystal part 21 to obtainthe converted beam having the wavelength of about 532 nm ½ times as longas the above-described wavelength.

[0046] Further, the rest of the basic beam having the wavelength of 1064nm whose wavelength is not converted in the second crystal part 21 isincident on the second selective transmitting film 24 and reflected onthe second selective transmitting film 24. Then, the rest of the basicbeam is repeatedly reflected between the first selective transmittingfilm 23 and the second selective transmitting film 24 until the basicbeam is converted to the converted beam having the wavelength of about532 nm.

[0047] Subsequently, the converted beam having the wavelength ofsubstantially 532 nm outputted from the second crystal part 21 isincident on the second selective transmitting film 24 and passes throughthe second selective transmitting film 24. Then, the converted beam isincident on the emitting lens 12 and emitted from the laser pointer 1 toa desired position so as to have a prescribed beam form.

[0048] As described above, in the laser pointer 1 according to thepresent invention, the laser beam having the wavelength of about 808 nmemitted from the semiconductor laser 10 is converted to the basic beamhaving the wavelength of about 1064 nm, then converted to the convertedbeam having the wavelength of about 532 nm, and the converted beam isoutputted.

[0049] Now, the adhesive layer 22 will be described in more detail.

[0050] The adhesive layer 22 is formed, as described above, byirradiating the acrylic adhesive having the glass transition point Tg ofabout 75° C. or lower with the ultraviolet rays or the visible rays andby curing the adhesive, and has the refractive index of 1.52 or lower.

[0051] Here, the acrylic adhesive indicates an adhesive that adhesivemolecules with molecular structures including functional groups composedof acrylic acid derivatives such as acrylate groups, methacrylategroups, urethane acrylate groups, etc. are bonded together and cured bya radical polymerization, an anionic polymerization, a cationicpolymerization or the like at double bonds included in the acrylic acidderivatives.

[0052] As the adhesives used for the adhesive layer 22, Sample 1 toSample 34 shown in the following Table 1 were used. Thus, the separationof the adhesive layer 22 and the damage of the first crystal part 20and/or the second crystal part 21 which were generated when the laserbeam with a prescribed output was emitted to the wavelength convertingelement 11 were judged. Then, the adhesives having good judgment resultswere used. The results of the Table 1 are shown as a graph in FIG. 2. ◯shown in the table and FIG. 2 designates that there is no separation ofthe adhesive layer 22, nor the damage of the first crystal part 20and/or the second crystal part 21. × indicates that there is theseparation of the adhesive layer 22 or the damage of the first crystalpart 20 and/or the second crystal part 21. TABLE 1 Refractive MakerModel Kind Tg (° C.) Index Judgment Sample 1 Adell UT-20 Acryl 112 1.52x Sample 2 Adell V300 Acryl — 1.52 x Sample 3 Adell HV153 Acryl — 1.63 xSample 4 Adell HR154 Acryl — — x Sample 5 Chemitec U471 Acryl 30 1.49 ∘Sample 6 Daikin UV3000 Acryl 100 1.498 x Sample 7 Dena XNR5472F Acryl 23— x Sample 8 Dena XNR5520 Acryl 34 — x Sample 9 Dena T695/UR Acryl 75 —x Sample Denka OP1080L Acryl −8 1.544 x 10 Sample Denka OP1030K Acryl 81.555 x 11 Sample Denka OP1030M Acryl 7 1.548 x 12 Sample Denka OP1030MSAcryl 15 1.548 x 13 Sample Denka OP3010P Acryl — — x 14 Sample Loctite363 Acryl — — x 15 Sample Sunrise PH150 Acryl −19 1.502 ∘ 16 SampleSunrise PH300 Acryl −20.8 1.505 ∘ 17 Sample Kyoritsu 801seL6 Acryl 3 ∘18 Sample Kyoritsu XVL90 Acryl 66 1.518 ∘ 19 Sample Kyoritsu 8807L5Acryl 62.7 1.518 ∘ 20 Sample Kyoritsu X8750LK5 Acryl 37 1.616 x 21Sample Daikin UV3100 Epoxy 130 — x 22 Sample Daikin UV3200 Epoxy 162 — x23 Sample Daikin UV4000 Epoxy 52 1.567 x 24 Sample Dena XNR5507FL Epoxy180 — x 25 Sample EMI 3505 Epoxy 150 1.5152 x 26 Sample EMI 3507 Epoxy142 1.56 x 27 Sample EpoTek OG146 Epoxy 75 1.4767 x 28 Sample NorlandNOA61 Epoxy 30 — x 29 Sample Norland NOA71 Epoxy 30 1.56 x 30 SampleNorland NOA73 Epoxy 30 1.56 x 31 Sample Norland NOA81 Epoxy 30 1.56 x 32Sample Norland NOA88 Epoxy 30 1.56 x 33 Sample Tree TB3121 Epoxy 41 — x34 Bond

[0053] The adhesives shown in the Sample 1 to the Sample 4 are acrylicadhesives which are respectively UT-20 (trade name), V300 (trade name),HV153 (trade name) and HR154 (trade name) produced by Adell Co., Ltd.The adhesive shown in the Sample 5 is an acrylic adhesive which is U471(trade name) produced by Chemitec Co., Ltd. The adhesive shown in theSample 6 is an acrylic adhesive which is UV3000 (trade name) produced byDaikin Industries, Ltd. The adhesives shown in the Sample 7 to theSample 9 are acrylic adhesives which are respectively XNR5472F (tradename), XNR5520 (trade name) and T695/UR (trade name) produced by Nagase& Co., Ltd (DENA). The adhesives shown in the Sample 10 to the Sample 14are acrylic adhesives which are respectively OP1080L (trade name),OP1030K (trade name), OP1030M (trade name), OP1030MS (trade name) andOP3010P (trade name) produced by Denki Kagaku Kogyo (DENKA) K. K. Theadhesive shown in the Sample 15 is an acrylic adhesive which is 363(trade name) produced by Henkel Japan Ltd. The adhesives shown in theSample 16 and the Sample 17 are acrylic adhesives which are respectivelyPH150 (trade name) and PH300 (trade name) produced by Sunrise MSICorporation. The adhesives shown in the Sample 18 to the Sample 21 areacrylic adhesives which are respectively 801seL6 (trade name), XVL90(trade name), 8807L5 (trade name) and X8750LK5 (trade name) produced byKyoritsu Chemical & Co., Ltd.

[0054] The adhesives shown in the Sample 22 to the Sample 24 are epoxyadhesives which are UV3100 (trade name), UV3200 (trade name) and UV4000(trade name) respectively produced by Daikin Industries, Ltd. Theadhesive shown in the Sample 25 is an epoxy adhesive which is XNR5507FLproduced by Nagase & Co., Ltd. (DENA).

[0055] The adhesives shown in the sample 26 and the Sample 27 are epoxyadhesive which are 3505 (trade name) and 3507 (trade name) produced bySAN-EI TECH (EMI) Co., Ltd. The adhesive shown in the Sample 28 is anepoxy adhesive which is OG146 (trade name) produced by Daizo (EPOTEK)Corporation. The adhesives shown in the Sample 29 to the Sample 33 areepoxy adhesives which are NOA61 (trade name), NOA71 (trade name), NOA73(trade name), NOA81 (trade name) and NOA 88 (trade name) respectivelyproduced by SAN-EI TECH (NORLAND) Co., Ltd. The adhesive shown in theSample 34 is an epoxy adhesive which is TB3121 (trade name) produced byThree bond Co., Ltd.

[0056] As apparent from the Table 1 and FIG. 2, the acrylic adhesivesinclude the Samples in which the separation of the adhesive layer 22 orthe damage of the first crystal element 20 and/or the second crystalpart 21 are not generated. On the other hand, in the epoxy adhesives,the separation of the adhesive layer 22 or the damage of the firstcrystal part 20 and the second crystal part 21 are generated in all theSamples.

[0057] Now, in accordance with the Table 1, the acrylic adhesives havinggood judgment results are extracted. Thus, a graph showing the relationbetween the glass transition point Tg of each Sample and the separationof the adhesive layer 22 and the damage of the crystal parts is shown inFIG. 3. ◯ indicates that the separation of the adhesive layer 22 or thedamage of the first crystal part 20 and/or the second crystal part 21does not exist. × indicates that the separation of the adhesive layer 22or the damage of the first crystal part 20 and/or the second crystalpart 21 is generated. Further, the sequence of the respective Samples inFIG. 3 shows that only the acrylic adhesives of the Samples shown in theTable 1 are rearranged in order of glass transition point Tg.

[0058] In FIG. 3, the glass transition point Tg of each Sample is paidattention to. In the adhesives having the glass transition point Tg of75° C. or lower, there are Samples in which the peeling-off of theadhesive layer 22 or the damage of the first crystal part 20 and/or thesecond crystal part 21 is not generated. On the other hand, in theadhesives having the glass transition point Tg of 75° C. or higher, thepeeling-off of the adhesive layer 22 or the damage of the first crystalpart 20 and the second crystal part 21 is generated in all the Samples.

[0059] Now, in accordance with the results shown in FIG. 3, the acrylicadhesives having good judgment results and the grass transition point of75° C. or lower are extracted. Thus, a graph showing the relationbetween the refractive index nD of each Sample and the separation of theadhesive layer 22 and the damage of the crystal parts is shown in FIG.4. In FIG. 4, ◯ indicates that the separation of the adhesive layer 22or the damage of the first crystal part 20 and/or the second crystalpart 21 does not exist. × indicates that the separation of the adhesivelayer 22 or the damage of the first crystal part 20 and/or the secondcrystal part 21 is generated. Further, the sequence of the respectiveSamples in FIG. 4 shows that only the acrylic Samples having the grasstransition point of 75° C. or lower shown in the Table 1 are rearrangedin order of refractive index nD.

[0060] In FIG. 4, the refractive index nD of each Sample is paidattention to. In the adhesives having the refractive index nD of 1.52 orlower, the peeling-off of the adhesive layer 22 or the damage of thefirst crystal part 20 and/or the second crystal part 21 is not generatedin all the Samples. On the other hand, in the adhesives having therefractive index nD higher than 1.52, the peeling-off of the adhesivelayer 22 or the damage of the first crystal part 20 and/or the secondcrystal part 21 is generated in all the Samples.

[0061] As apparent from the results shown in the Table 1 and FIGS. 2 to4, as the adhesive forming the adhesive layer 22, an acrylic adhesivehaving conditions of light transmitting characteristics and the glasstransition point Tg of about 75° C. or lower, and the refractive indexof about 1.52 or lower after the adhesive is irradiated with ultravioletrays or visible rays to be cured is obviously preferable.

[0062] Specifically, as the adhesive forming the adhesive layer 22, theSamples 5, 16, 17, 19 and 20 shown in the Table 1 are preferable andthey completely satisfy all the above-described conditions.

[0063] As described above, the adhesive layer 22 is formed byirradiating the acrylic adhesive having the light transmittingcharacteristics and the glass transition point Tg of about 75° C. orlower with the ultraviolet rays or the visible rays to be cured, and hasthe refractive index of 1.52 or lower after the adhesive is cured.

[0064] In the laser pointer 1 constructed as described above, theadhesive selected as described above is employed for the wavelengthconverting element 11. Accordingly, the generation of the separation ofthe adhesive layer 22 or the damage of the first crystal part 20 and/orthe second crystal part 21 can be suppressed. Thus, the life of aproduct can be extended and the reliability of a product can beimproved.

[0065] Further, in the laser pointer 1, the generation of the separationof the adhesive layer 22 or the damage of the first crystal part 20and/or the second crystal part 21 can be suppressed. Accordingly, thelaser beam of a higher output can be inputted and the output of theconverted beam can be improved.

[0066] Further, in the laser pointer 1, the wavelength band of theconverted beam, that is, the outputted laser beam can be converted tothe green wavelength band high in its visibility. Accordingly, a brightand clear laser beam can be outputted even under a low output relativeto a usual laser beam of a red wavelength band to improve the safety inuse.

[0067] Still further, in the laser pointer 1, since the optical elementsare bonded together to form the wavelength converting element 11 asdescribed above, a simple device in which the number of parts can bereduced and an adjustment is not necessary can be obtained. Thus, amanufacture cost can be reduced.

[0068] In the above-described laser pointer 1, the structure of thedevice in which the converted beam has the wavelength of about 532 nm isexplained. However, the features or the qualities of the semiconductorlaser 10, the first crystal part 20 and the second crystal part 21, andthe first selective transmitting film 23 and the second selectivetransmitting film 24 may be selected in accordance with the desiredwavelength band of the converted beam. Further, the first crystal part20 and the second crystal part 21 may be doped with dopant such as Ndhaving arbitrary concentration and may be set depending on use. Further,the first crystal part 20 and the second crystal part 21 may be formedin a flat shape, a curved shape or a spherical shape and may belaminated in layers. However, they are not limited to these shapes.

[0069] Now, a method for producing the wavelength converting element 11used for the above-described laser pointer 1 will be described below.

[0070] Initially, a wafer of the first crystal part 20 and a wafer ofthe second crystal part 21 are optically polished so that their surfacesopposed to each other whose coefficients of linear expansion aredifferent by 5 ppm or more include their crystallographic axes.

[0071] Then, the above-described adhesive is applied to the opposedsurface of the wafer of the first crystal part 20 or the wafer of thesecond crystal part 21 to stick the wafer of the first crystal part 20to the wafer of the second crystal part 21. The adhesive is irradiatedwith light to cure the adhesive and form the adhesive layer 22.

[0072] Subsequently, the first selective transmitting film 23 and thesecond selective transmitting film 24 are respectively formed onsurfaces opposite to the adhesive layer 22 of the wafer of the firstcrystal part 20 and the wafer of the second crystal part 21. Then, theobtained part is cut to a desired size.

[0073] The wavelength converting element 11 is produced as describedabove. Specifically, the wavelength converting element 11 will bedescribed in accordance with Example 1 to Example 24 and ComparativeExample 1 to Comparative Example 13. TABLE 2 First Crystal part/SecondIntensity of Light Crystal part Adhesive (mW/cm²) Example 1 KTP/YVO₄Sample 20 1 Example 2 KTP/YVO₄ Sample 17 1 Example 3 KTP/YVO₄ Sample 205 Example 4 KTP/YVO₄ Sample 17 5 Example 5 KTP/YVO₄ Sample 20 1 Example6 KTP/YVO₄ Sample 17 1 Example 7 KTP/YVO₄ Sample 20 5 Example 8 KTP/YVO₄Sample 17 5 Example 9 Quartz/Glass Sample 20 1 Example 10 Quartz/GlassSample 17 1 Example 11 Quartz/Glass Sample 20 5 Example 12 Quartz/GlassSample 17 5 Example 13 Quartz/Glass Sample 20 1 Example 14 Quartz/GlassSample 17 1 Example 15 Quartz/Glass Sample 20 5 Example 16 Quartz/GlassSample 17 5 Example 17 YVO₄/Quartz Sample 20 1 Example 18 YVO₄/QuartzSample 17 1 Example 19 YVO₄/Quartz Sample 20 5 Example 20 YVO₄/QuartzSample 17 5 Example 21 YVO₄/Quartz Sample 20 1 Example 22 YVO₄/QuartzSample 17 1 Example 23 YVO₄/Quartz Sample 20 5 Example 24 YVO₄/QuartzSample 17 5 Comparative KTP/YVO₄ Sample 1 1 example 1 ComparativeKTP/YVO₄ Sample 10 1 Example 2 Comparative KTP/YVO₄ Sample 28 1 Example3 Comparative Quartz/Glass Sample 1 1 Example 4 Comparative Quartz/GlassSample 10 1 Example 5 Comparative Quartz/Glass Sample 28 1 Example 6Comparative YVO₄/Quartz Sample 1 1 Example 7 Comparative YVO₄/QuartzSample 10 1 Example 8 Comparative YVO₄/Quartz Sample 28 1 Example 9Comparative KTP/YVO₄ Sample 20 20 Example 10 Comparative KTP/YVO₄ Sample17 20 Example 11 Comparative KTP/YVO₄ Sample 20 1 Example 12 ComparativeKTP/YVO₄ Sample 17 1 Example 13

[0074] Thickness 150° C./ 200° C./ 250° C./ (μm) 100 H 4 H 4 H Example 16 ∘ ∘ ∘ Example 2 6 ∘ ∘ ∘ Example 3 6 ∘ ∘ ∘ Example 4 6 ∘ ∘ ∘ Example 53 ∘ ∘ ∘ Example 6 3 ∘ ∘ ∘ Example 7 3 ∘ ∘ ∘ Example 8 3 ∘ ∘ ∘ Example 96 ∘ ∘ ∘ Example 10 6 ∘ ∘ ∘ Example 11 6 ∘ ∘ ∘ Example 12 6 ∘ ∘ ∘ Example13 3 ∘ ∘ ∘ Example 14 3 ∘ ∘ ∘ Example 15 3 ∘ ∘ ∘ Example 16 3 ∘ ∘ ∘Example 17 6 ∘ ∘ ∘ Example 18 6 ∘ ∘ ∘ Example 19 6 ∘ ∘ ∘ Example 20 6 ∘∘ ∘ Example 21 3 ∘ ∘ ∘ Example 22 3 ∘ ∘ ∘ Example 23 3 ∘ ∘ ∘ Example 243 ∘ ∘ ∘ Comparative 6 x x x example 1 Comparative 6 Δ x x Example 2Comparative 6 Δ x x Example 3 Comparative 6 x x x Example 4 Comparative6 Δ x x Example 5 Comparative 6 Δ x x Example 6 Comparative 6 x x xExample 7 Comparative 6 Δ x x Example 8 Comparative 6 Δ x x Example 9Comparative 6 ∘ ∘ Δ Example 10 Comparative 6 ∘ ∘ Δ Example 11Comparative 2 ∘ ∘ Δ Example 12 Comparative 2 ∘ ∘ Δ Example 13

[0075] In 150° C./100 H in the Table 2, the wavelength convertingelements 11 formed in the Example 1 to the Example 24 and theComparative Example 1 to the Comparative Example 13 were stored in aconstant temperature bath whose temperature was controlled to 150° C.for 100 hours. Then, the separation of the adhesive layers 22 wasobserved.

[0076] In 200° C./4 H in the Table 2, the wavelength converting elements11 formed in the Example 1 to the Example 24 and the Comparative Example1 to the Comparative Example 13 were stored in a constant temperaturebath whose temperature was controlled to 200° C. for 4 hours. Then, theseparation of the adhesive layers 22 was observed.

[0077] Further, in 250° C./4 H in the Table 2, the wavelength convertingelements 11 formed in the Example 1 to the Example 24 and theComparative Example 1 to the Comparative Example 13 were stored in aconstant temperature bath whose temperature was controlled to 250° C.for 4 hours. Then, the separation of the adhesive layers 22 wasobserved.

[0078] ◯ illustrated in the Table 2 shows that the separation of theadhesive layer 22 is not generated. Δ indicates that a part of theadhesive layer 22 is peeled off. × indicates that a half or more of theadhesive layer 22 is peeled off.

EXAMPLE 1

[0079] In the Example 1, the wafer of a KTP crystal having asubstantially rectangular shape of about 1.5 cm×3.0 cm which was cut atan phase matching angle and a wafer obtained by cutting a wafer of aYVO₄ crystal formed in a substantially circular shape with the diameterof about 2.5 cm which was cut on a plane including an a-axis, that is,an a-plane to a half in the direction inclined by 45° relative to ac-axis were respectively optically polished with an accuracysufficiently necessary for a laser oscillation.

[0080] Then, the adhesive of the above-described Sample 20 was appliedto the adhesive surface of the optically polished wafer of the KTPcrystal to stick the KTP crystal to the YVO₄ crystal so that the c-axisof the KTP crystal and the c-axis of the YVO₄ crystal were inclined by45°. Here, the amount of application of the adhesive was adjusted sothat the thickness of the adhesive layer 22 was 6 μm.

[0081] Then, the adhesive was irradiated with ultraviolet rays havingthe intensity of light of 1 mW/cm² to cure the adhesive.

EXAMPLE 2

[0082] In the Example 2, the wavelength converting element 11 was formedand the adhesive layer 22 in the formed wavelength converting element 11was observed under the same conditions as those of the Example 1 exceptthat a Sample 17 was used for the adhesive.

EXAMPLE 3

[0083] In the Example 3, the wavelength converting element 11 was formedand the adhesive layer 22 in the formed wavelength converting element 11was observed under the same conditions as those of the Example 1 exceptthat the adhesive was irradiated with ultraviolet rays having theintensity of light of 5 mW/cm² to cure the adhesive.

EXAMPLE 4

[0084] In the Example 4, the wavelength converting element 11 was formedand the adhesive layer 22 in the formed wavelength converting element 11was observed under the same conditions as those of the Example 3 exceptthat a Sample 17 was used for the adhesive.

EXAMPLE 5

[0085] In the Example 5, the wavelength converting element 11 was formedand the adhesive layer 22 in the formed wavelength converting element 11was observed under the same conditions as those of the Example 1 exceptthat the thickness of the adhesive layer 22 was 3 μm.

EXAMPLE 6

[0086] In the Example 6, the wavelength converting element 11 was formedand the adhesive layer 22 in the formed wavelength converting element 11was observed under the same conditions as those of the Example 5 exceptthat a Sample 17 was used for the adhesive.

EXAMPLE 7

[0087] In the Example 7, the wavelength converting element 11 was formedand the adhesive layer 22 in the formed wavelength converting element 11was observed under the same conditions as those of the Example 1 exceptthat the adhesive was irradiated with ultraviolet rays having theintensity of light of 5 mW/cm² to cure the adhesive and the thickness ofthe adhesive layer 22 was 3 μm.

EXAMPLE 8

[0088] In the Example 8, the wavelength converting element 11 was formedand the adhesive layer 22 in the formed wavelength converting element 11was observed under the same conditions as those of the Example 7 exceptthat a Sample 17 was used for the adhesive.

EXAMPLE 9

[0089] In the Example 9, the wavelength converting element 11 was formedand the adhesive layer 22 in the formed wavelength converting element 11was observed under the same conditions as those of the Example 1 exceptthat a quartz plate having the thickness of about 1 mm and asubstantially square shape of about 15 mm×15 mm and a BK7 optical glasshaving the thickness of about 2 mm and a substantially rectangular shapeof about 19 mm×25 mm were optically polished and stuck together.

EXAMPLE 10

[0090] In the Example 10, the wavelength converting element 11 wasformed and the adhesive layer 22 in the formed wavelength convertingelement 11 was observed under the same conditions as those of theExample 9 except that a Sample 17 was used for the adhesive.

EXAMPLE 11

[0091] In the Example 11, the wavelength converting element 11 wasformed and the adhesive layer 22 in the formed wavelength convertingelement 11 was observed under the same conditions as those of theExample 9 except that the adhesive was irradiated with ultraviolet rayshaving the intensity of light of 5 mW/cm² for curing the adhesive.

EXAMPLE 12

[0092] In the Example 12, the wavelength converting element 11 wasformed and the adhesive layer 22 in the formed wavelength convertingelement 11 was observed under the same conditions as those of theExample 11 except that a Sample 17 was used for the adhesive.

EXAMPLE 13

[0093] In the Example 13, the wavelength converting element 11 wasformed and the adhesive layer 22 in the formed wavelength convertingelement 11 was observed under the same conditions as those of theExample 9 except that the thickness of the adhesive layer was 3 μm.

EXAMPLE 14

[0094] In the Example 14, the wavelength converting element 11 wasformed and the adhesive layer 22 in the formed wavelength convertingelement 11 was observed under the same conditions as those of theExample 13 except that a Sample 17 was used for the adhesive.

EXAMPLE 15

[0095] In the Example 15, the wavelength converting element 11 wasformed and the adhesive layer 22 in the formed wavelength convertingelement 11 was observed under the same conditions as those of theExample 9 except that the adhesive was irradiated with ultraviolet rayshaving the intensity of light of 5 mW/cm² for curing the adhesive andthe thickness of the adhesive layer 22 was 3 μm.

EXAMPLE 16

[0096] In the Example 16, the wavelength converting element 11 wasformed and the adhesive layer 22 in the formed wavelength convertingelement 11 was observed under the same conditions as those of theExample 15 except that a Sample 17 was used for the adhesive.

EXAMPLE 17

[0097] In the Example 17, the wavelength converting element 11 wasformed and the adhesive layer 22 in the formed wavelength convertingelement 11 was observed under the same conditions as those of theExample 1 except that a wafer obtained by cutting a wafer of a YVO₄crystal formed in a substantially circular shape with the diameter ofabout 2.5 cm which was cut on an a-plane to a half and a quartz platehaving a substantially rectangular shape of about 1.5 cm×3.0 cm wererespectively optically polished and stuck together with an accuracysufficiently necessary for a laser oscillation.

[0098] When the YVO₄ crystal is stuck to the quartz plate, thedifference in coefficient of linear expansion between them is large asrepresented by 11.37 (c-axis of YVO₄)−0.58 (quartz)=9.78 ppm.

EXAMPLE 18

[0099] In the Example 18, the wavelength converting element 11 wasformed and the adhesive layer 22 in the formed wavelength convertingelement 11 was observed under the same conditions as those of theExample 17 except that a Sample 17 was used for the adhesive.

EXAMPLE 19

[0100] In the Example 19, the wavelength converting element 11 wasformed and the adhesive layer 22 in the formed wavelength convertingelement 11 was observed under the same conditions as those of theExample 17 except that the adhesive was irradiated with ultraviolet rayshaving the intensity of light of 5 mW/cm² for curing the adhesive.

EXAMPLE 20

[0101] In the Example 20, the wavelength converting element 11 wasformed and the adhesive layer 22 in the formed wavelength convertingelement 11 was observed under the same conditions as those of theExample 19 except that a Sample 17 was used for the adhesive.

EXAMPLE 21

[0102] In the Example 21, the wavelength converting element 11 wasformed and the adhesive layer 22 in the formed wavelength convertingelement 11 was observed under the same conditions as those of theExample 17 except that the thickness of the adhesive layer 22 was 3 μm.

EXAMPLE 22

[0103] In the Example 22, the wavelength converting element 11 wasformed and the adhesive layer 22 in the formed wavelength convertingelement 11 was observed under the same conditions as those of theExample 21 except that a Sample 17 was used for the adhesive.

EXAMPLE 23

[0104] In the Example 23, the wavelength converting element 11 wasformed and the adhesive layer 22 in the formed wavelength convertingelement 11 was observed under the same conditions as those of theExample 17 except that the adhesive was irradiated with ultraviolet rayshaving the intensity of light of 5 mW/cm² for curing the adhesive andthe thickness of the adhesive layer 22 was 3 μm.

EXAMPLE 24

[0105] In the Example 24, the wavelength converting element 11 wasformed and the adhesive layer 22 in the formed wavelength convertingelement 11 was observed under the same conditions as those of theExample 23 except that a Sample 17 was used for the adhesive.

COMPARATIVE EXAMPLE 1

[0106] In the Comparative Example 1, the wavelength converting element11 was formed and the adhesive layer 22 in the formed wavelengthconverting element 11 was observed under the same conditions as those ofthe Example 1 except that a Sample 1 was used for the adhesive.

COMPARATIVE EXAMPLE 2

[0107] In the Comparative Example 2, the wavelength converting element11 was formed and the adhesive layer 22 in the formed wavelengthconverting element 11 was observed under the same conditions as those ofthe Example 1 except that a Sample 10 was used for the adhesive.

COMPARATIVE EXAMPLE 3

[0108] In the Comparative Example 3, the wavelength converting element11 was formed and the adhesive layer 22 in the formed wavelengthconverting element 11 was observed under the same conditions as those ofthe Example 1 except that a Sample 28 was used for the adhesive.

COMPARATIVE EXAMPLE 4

[0109] In the Comparative Example 4, the wavelength converting element11 was formed and the adhesive layer 22 in the formed wavelengthconverting element 11 was observed under the same conditions as those ofthe Example 9 except that a Sample 1 was used for the adhesive.

COMPARATIVE EXAMPLE 5

[0110] In the Comparative Example 5, the wavelength converting element11 was formed and the adhesive layer 22 in the formed wavelengthconverting element 11 was observed under the same conditions as those ofthe Example 9 except that a Sample 10 was used for the adhesive.

COMPARATIVE EXAMPLE 6

[0111] In the Comparative Example 6, the wavelength converting element11 was formed and the adhesive layer 22 in the formed wavelengthconverting element 11 was observed under the same conditions as those ofthe Example 9 except that a Sample 28 as used for the adhesive.

COMPARATIVE EXAMPLE 7

[0112] In the Comparative Example 7, the wavelength converting element11 was formed and the adhesive layer 22 in the formed wavelengthconverting element 11 was observed under the same conditions as those ofthe Example 17 except that a Sample 1 was used for the adhesive.

COMPARATIVE EXAMPLE 8

[0113] In the Comparative Example 8, the wavelength converting element11 was formed and the adhesive layer 22 in the formed wavelengthconverting element 11 was observed under the same conditions as those ofthe Example 17 except that a Sample 10 as used for the adhesive.

COMPARATIVE EXAMPLE 9

[0114] In the Comparative Example 9, the wavelength converting element11 was formed and the adhesive layer 22 in the formed wavelengthconverting element 11 was observed under the same conditions as those ofthe Example 17 except that a Sample 28 as used for the adhesive.

COMPARATIVE EXAMPLE 10

[0115] In the Comparative Example 10, the wavelength converting element11 was formed and the adhesive layer 22 in the formed wavelengthconverting element 11 was observed under the same conditions as those ofthe Example 1 except that the adhesive was irradiated with ultravioletrays having the intensity of light of 20 mW/cm² for curing the adhesive.

COMPARATIVE EXAMPLE 11

[0116] In the Comparative Example 11, the wavelength converting element11 was formed and the adhesive layer 22 in the formed wavelengthconverting element 11 was observed under the same conditions as those ofthe Example 10 except that a Sample 17 was used for the adhesive.

COMPARATIVE EXAMPLE 12

[0117] In the Comparative Example 12, the wavelength converting element11 was formed and the adhesive layer 22 in the formed wavelengthconverting element 11 was observed under the same conditions as those ofthe Example 1 except that the thickness of the adhesive layer 22 was 2μm.

COMPARATIVE EXAMPLE 13

[0118] In the Comparative Example 13, the wavelength converting element11 was formed and the adhesive layer 22 in the formed wavelengthconverting element 11 was observed under the same conditions as those ofthe Comparative Example 12 except that a Sample 17 was used for theadhesive.

[0119] In the results of the Table 2, when the acrylic adhesive havingfeatures that the glass transition point Tg of the adhesive was 75° C.or lower and the refractive index nD of the cured material of theadhesive was 1.52 or lower was used, the adhesive layer 22 was notpeeled off under the conditions of 150° C./100 H and 200° C./4 H.Further, under the condition of 250° C./4 H as a more severe condition,when the intensity of light of ultraviolet ray was 5 mW/cm² or lower andthe thickness of the film was 3 μm or more, the separation of theadhesive layer 22 or the like was not generated.

[0120] On the other hand, the adhesive having the glass transition pointTg higher than 75° C., the adhesive having the refractive index nDhigher than 1.52, or the epoxy adhesive could not maintain a sufficientadhesion under any of the conditions of 150° C./100 H, 200° C./4 H and250° C./4 H, and the adhesive layer 22 was peeled off.

[0121] As apparent from the results shown in the Table 2, the acrylicadhesives having the glass transition point Tg of 75° C. or lower couldmitigate a stress generated in the adhesive layer 22 due to a thermalexpansion. Further, it was understood that the adhesives which wereirradiated with the ultraviolet rays having the intensity of light of 5mW/cm² or lower to be cured were used so that the first crystal part 20and the second crystal part could be stuck to each other with highaccuracy without a curve due to the anisotropic characteristics of thefirst crystal part and the second crystal part owing to heat. Further,as apparent from the results shown in the Table 2, when the adhesive wasapplied so that the thickness of the adhesive layer 22 was 3 μm or more,the first crystal part and the second crystal part could be highlyaccurately stuck together without a curve due to the anisotropiccharacteristics of them owing to heat.

[0122] In the method for producing the wavelength converting element 11to which the present invention is applied, the crystal parts can bestuck to each other without a curve of the wafers due to the stress ofthe first selective transmitting film 23 and the second selectivetransmitting film 24. Accordingly, the adhesive layer 22 having uniformthickness can be obtained. Thus, the produced wavelength convertingelement 11 can not only improve various kinds of characteristics, butalso suppress unevenness in characteristics of the cut wavelengthconverting elements 11. Further, a large quantity of wavelengthconverting elements 11 having good qualities can be produced, so thatproductivity can be improved and a manufacture cost can be reduced.

[0123] As described above, the thickness of the adhesive layer 22 can beadjusted to be larger than 1 μm. However, when the thickness of the filmis large, the parallel accuracy of the film thickness of the adhesivelayer 22 is deteriorated. Therefore, the thickness of the adhesive layer22 is preferably 20 μm or smaller.

[0124] Further, in the above-described Examples, the adhesivesirradiated with the ultraviolet rays or the visible rays to be cured areused. It is to be understood that an adhesive heated to be cured may beused.

[0125] Further, as a condition of applying the ultraviolet rays or thevisible rays for curing the adhesive, a method for using an existinglight source such as a metal halide lamp, a black light lamp, a mercurylamp, natural light, etc. may be employed. Specifically, as theirradiation condition, the intensity of light ranging from 0.1 mW/cm² to200 mW/cm² may be used. As the irradiation conditions of the ultravioletrays or the visible rays, the adhesive is desirably irradiated with therays having the intensity of light of 0.1 mW/cm² and more and 5 mW/cm²or less and an amount of irradiation of rays designated by the maker. Toimprove the adhesive strength of the adhesive, a thermosetting step maybe performed after the irradiation with the ultraviolet rays or thevisible rays.

[0126] It is obvious for a person with ordinary skill in the art thatvarious changes, substitutions or equivalence thereto can be made in thepresent invention without departing the scope of the attached claims andthe gist thereof.

INDUSTRIAL APPLICABILITY

[0127] As described above, according to the present invention, in theoptical element, the first crystal part including KTiOPO₄ or quartz andthe second crystal part including YVO₄ doped with Nd in which opposedsurface have coefficients of linear expansion different by 5 ppm or moreare stuck together by using the acrylic adhesive having the glasstransition point of 75° C. or lower, and the refractive index of thecured material of the adhesive is 1.52 or lower. In the optical element,the adhesive layer mitigates the stress due to the difference in thermalexpansion. Thus, the separation of the adhesive layer from the firstcrystal part or the second crystal part, or the damage of the firstcrystal part or the second crystal part can be suppressed.

[0128] Therefore, the reliability of the optical element is improved andthe input beam with high output can be met.

1. An optical element for converting light of prescribed wavelengthemitted from a light source into light of wavelength different from theprescribed wavelength for outputting; the optical element comprising: afirst crystal part including KTiOPO₄ or quartz; a second crystal partincluding YVO₄ doping Nd; and an adhesive layer by which the firstcrystal part is stuck to the second crystal part, wherein surfaces ofthe first crystal part and the second crystal part opposed to each otherthrough the adhesive layer have coefficients of linear expansion whichare different by 5 ppm or more and the surfaces opposed to each otherthrough the adhesive layer are disposed so as to includecrystallographic axes, and the adhesive layer is formed by curing anacrylic adhesive whose glass transition point is 75° C. or lower byapplying light to the adhesive, the refractive index of the adhesivelayer after cure being 1.52 or lower.
 2. The optical element accordingto claim 1, wherein the adhesive layer is formed by curing the adhesiveby irradiating the adhesive with ultraviolet rays or visible rays havingan output of 5 mW/cm² or lower.
 3. The optical element according toclaim 1, wherein the adhesive layer has its thickness of 3 μm or larger.4. The optical element according to claim 1, further including a pair ofoptical films for transmitting light whose wavelength is converted intowavelength different from the prescribed wavelength and reflecting thelight whose wavelength is not converted.
 5. A light emitting devicecomprising: a light source for emitting light of prescribed wavelength;and an optical element including a first crystal part including KTiOPO₄or quartz; a second crystal part including YVO₄ doping Nd; and anadhesive layer by which the first crystal part is stuck to the secondcrystal part; the optical element converting light of wavelength emittedfrom the light source into light of wavelength different from theprescribed wavelength for outputting, wherein surfaces of the firstcrystal part and the second crystal part opposed to each other throughthe adhesive layer have coefficients of linear expansion which aredifferent by 5 ppm or more and the surfaces opposed to each otherthrough the adhesive layer are disposed so as to includecrystallographic axes, and the adhesive layer is formed by curing anacrylic adhesive whose glass transition point is 75° C. or lower byapplying light to the adhesive, the refractive index of the adhesivelayer after cure being 1.52 or lower.
 6. The light emitting deviceaccording to claim 5, wherein the adhesive layer is formed by curing theadhesive by irradiating the adhesive with ultraviolet rays or visiblerays having an output of 5 mW/cm² or lower.
 7. The light emitting deviceaccording to claim 5, wherein the adhesive layer has its thickness of 3μm or larger.
 8. The light emitting device according to claim 5, furtherincluding a pair of optical films for transmitting light whosewavelength is converted into wavelength different from the prescribedwavelength and reflecting the light whose wavelength is not converted.9. The light emitting device according to claim 5, further including anemitting lens for adjusting the form of a beam of the light which isoutputted from the optical element with its wavelength converted intowavelength different from the prescribed wavelength.
 10. A method forproducing an optical element for converting light of prescribedwavelength emitted from a light source into light of wavelengthdifferent from the prescribed wavelength for outputting; the methodcomprising: a polishing step of optically polishing a first crystal partincluding KTiOPO₄ or quartz and a second crystal part including YVO₄doping Nd so that surfaces opposed to each other have coefficients oflinear expansion different by 5 ppm or more and the surfaces opposed toeach other include crystallographic axes; an applying step of applyingan acrylic adhesive whose glass transition point is 75° C. or lower tothe surface of the first crystal part or the second crystal part; asticking step of allowing the first crystal part to abut on the secondcrystal part through the adhesive applied in the applying step andirradiating the adhesive with light to cure the adhesive, and form anadhesive layer having a refractive index of 1.52 or lower; and a cuttingstep of cutting the first crystal part and the second crystal part stuckto each other through the adhesive layer to a desired size.
 11. Themethod for producing an optical element according to claim 10, wherein,in the sticking step, the adhesive is irradiated with ultraviolet raysor visible rays having an output of 5 mW/cm² or lower.
 12. The methodfor producing an optical element according to claim 10, wherein, in theapplying step, the adhesive layer has its thickness of 3 μm or larger.13. The method for producing an optical element according to claim 10,further including, before the cutting step, a film forming step offorming a pair of optical films for transmitting the light whosewavelength is converted into wavelength different from the prescribedwavelength and reflecting the light whose wavelength is not convertedrespectively on the other surfaces opposite to the surfaces of the firstcrystal part and the second crystal part.